The fabrication of integrated circuits is typically done by building successive layers on top of each other. Many process steps are involved in fabrication including deposition, oxidation, planarization, etching, diffusion, implantation, and lithography. Lithography is an important part of the fabrication process and is used to transfer a desired pattern onto a surface. Conventional lithography typically uses a mask and photosensitive material known as “photoresist” to create the desired pattern. However, lithography may be used in many different ways, such as with or without photoresist, with or without some other energy-sensitive material, and in fabricating technologies such as semiconductors, liquid crystal displays, and micro-electromechanical systems.
The continuous and significant advances in the semiconductor industry have been due, in part, to many technical advances, such as improved lenses, improved photoresist materials, improved chemical-mechanical polishing, and others. The biggest improvements, however, may be in the area of lithography such as with the use of increasingly shorter wavelengths in the lithographic process. In general, shorter wavelengths provide better resolution but they create other problems and are more expensive to implement. Furthermore, physical limitations are presenting problems for the continued reduction in wavelengths in lithography.
Several solutions are being investigated for continued performance advances in semiconductor fabrication, such as electron projection lithography, immersion lithography, and extreme ultraviolet lithography. However, the proposed solutions require major advances in technology, such as light sources, resist materials, masks, and process controls. Furthermore, the costs of lithography and other fabrication processes and tools have increased dramatically, and the research and development required for major advances in various technologies will add to the costs.
U.S. Pat. No. 6,818,389, issued to Fritze et al, discloses a system and method in which repetitive structures are formed on a substrate and then a trim mask is used to modify the repetitive structure to a desired structure. This teaching, however, has several drawbacks. For example, at column 9, lines 57-67, the process requires a separate photoresist layer for each application of the repetitive structure.
Accordingly, there is a need for improved lithographic processes, particularly for processes which can offer high precision and cost savings. Those and other advantages of the present invention will be described in more detail hereinbelow.